As is well known, an umbrella is a device that protects the user from the elements and in particular from liquid and frozen precipitation or even the sun, etc. A traditional umbrella has the following parts: a pole, a canopy, ribs, a runner, springs and a ferrule. A pole is the metal or wooden shaft that runs between the umbrella's handle at the bottom (or the base stand in the case of a patio model) and the canopy at the top. The canopy is the fabric part of the umbrella that catches the rain, the wind and the sun. The ribs are what give an umbrella its structure and shape. Outer ribs hold up the canopy and inner ribs (sometimes called stretchers) act as supports and connect the outer ribs to the umbrella pole. A runner slides up and down the pole while connected to the ribs/stretchers, and is responsible for the opening and closing of the canopy. Many umbrella designs include a top spring to hold the runner up when the canopy is open, a bottom spring to hold the runner down when the canopy is closed, and sometimes a center ball spring to extend the pole length in telescopic models. Strictly ornamental, the finial (also called the ferrule) is found on the very top of the umbrella, above the canopy.
Umbrella ribs function in a folding construction supporting the umbrella canopy fabric. Under normal operating conditions, the forces acting on the umbrella canopy fabric increase toward peak values when the canopy becomes fully deployed and when wind gusts tend to overturn the canopy. These forces are transmitted from the canopy to the canopy ribs, and can act on the ribs in opposite directions depending on the direction of the wind. The ribs thus have to be strong enough to withstand forces which can act on them from anyone of the two main opposite directions.
In addition to their strength requirements, the shape of the umbrella ribs should change between a substantially straight contour when the umbrella is folded and a curved one, when the canopy if fully deployed. The straight design is aimed to allow the folded fibs to lay parallel to the shaft of the umbrella when the umbrella is folded and the curved design provides for the typical mushroom-like shape (also called bell shaped).